Sulphate-dependant microbially induced corrosion of mild steel in the deep-sea: a 10-year environmental study

Metal corrosion in seawater has been well studied in surface and shallow waters. However, infrastructure is increasingly being installed in deep-sea environments, where extremes of temperature, salinity and high hydrostatic pressure increase costs and logistical challenges of monitoring corrosion on structures and equipment. To improve the understanding of the performance of materials in the deep-sea, the corrosion, the composition and the functional capacity of the microbial community on the surface of mooring chain links deployed for 10 years at ~2km depth was studied. The high corrosion rate and the form of corrosion (deep pitting) suggest that the corrosion of the mooring chain links was driven by both abiotic and biotic processes. The microbial community on the surface of the chain links differed considerably from that of the surrounding sediment or sea water, suggesting selection for a specific metal-corroding biofilms. The results indicate that deep-sea sulfur cycling microorganisms may gain energy by accelerating the reaction between metallic iron and elemental sulfur, which would otherwise take place more slowly, thus accounting for the high corrosion rate detected. The results of this field study also provide new insights on the effects of high hydrostatic pressure on microbially induced corrosion in seawater.